In electrical systems we know that current produces a magnetic field. If you have two parallel wires carrying DC current in the same direction they will attract each other with magnetism.

A moving charge is the same thing as current. In fact current is a result of moving charges. We know that moving charged particles have their own magnetic field.

Consider the first example but this time lets say that instead of wires you have two like charged particles moving in the same direction. Like before they should exert an attractive magnetic force on one another.

Now lets throw a wrench into this logic.

If you were traveling with these two particles so you were moving with the same speed and direction, you are in their reference frame. Now because both reference frames are inertial (non accelerating) we know they are equivalent.

The charged particles are not moving with respect to one another. They are no longer producing a magnetic field. They should repel one another. How is this possible?

The attraction is between the medium through which the charge travels, not the charge itself. So if you had two particles traveling together (tough to do with no medium) they wouldn't have a positive or negative charge.

its not quantum physics. the answer is subtle. really though all you need to do is google the relevant equations and do some very basic algebra, or you could use some slightly more advanced theories to explain what is going on verbaly. Like hacking there are many approaches to solve the puzzle

circuitboardsushi wrote:its not quantum physics. the answer is subtle. really though all you need to do is google the relevant equations and do some very basic algebra, or you could use some slightly more advanced theories to explain what is going on verbaly. Like hacking there are many approaches to solve the puzzle

The thing with this question is that a single moving charge does not constitute a current. For example, using current density J to express current as I = J (scalar dot product) A. Since the charge passing through any plane A is 0 except for at the exact moment your single charge passes through it you essentially have 0 current density and therefore no current. Therefore the equations used to prove attraction between two conductors with same direction DC current flowing through them cannot be used, you are more likely to get a useful result from looking up maxwells equations